1. Field of the Invention
The present general inventive concept relates to a power supply device, and an image forming apparatus having the same, and more particularly, to a power supply device to supply driving voltages to the component units of an image forming apparatus using a reduced number of transformers, and to adjust an amplitude of each of the driving voltages independently, and an image forming apparatus having the power supply device.
2. Description of the Related Art
Many electronic apparatuses generally employ a switching mode power supply (SMPS), which switches rectified and smoothed DC current derived from an AC utility source into high frequency, such as 100 kHz, to convert the power into a DC current of a different amplitude by a transformer.
Controlling the output power of the switching mode power supply generally includes pulse width modulation (PWM) control, which controls the duty cycle of switching pulses according to the desired output power, a frequency control, which controls the frequency of the switching pulses, and a phase control which controls the phase of the switching pulse.
In color printing applications, pulse width modulation is very effective in controlling transfer of color images.
One image forming apparatus includes a plurality of components, including a charger, a light exposure unit, a developer, a transfer unit, a fuser, and the like. Some of these components such as the charger and the transfer unit require a high DC driving voltage to operate. Each of the charger and the transfer unit requires a different level of power, so each level of power is typically supplied from different power supplies.
FIGS. 1A and 1B are block diagrams of conventional PWM control type power supplies. Referring to FIGS. 1A and 1B, different power supplies are provided to each of the different components and supply different levels of driving voltages as required by those components. In particular, FIG. 1A illustrates a power supply to supply driving voltage to a photoconductive medium charger, and FIG. 1B illustrates a power supply to supply driving voltage to a transfer unit.
Referring first to FIG. 1A, a power supply 10 to generate a charging voltage includes a PWM controller 11, a comparer 12, a switching transformer 13, a voltage doubler unit 14, and a charging power output unit 15.
The PWM controller 11 transmits a PWM control signal to the comparer 12 according to the level of voltage needed to perform the charging of an organic photoconductive (OPC) medium. The comparer 12 applies power to the switching transformer 13 by alternating between on and off states according to the control signal being input. The switching transformer 13 converts the alternating voltage into a level needed in the charger. Next, the voltage doubler unit 14 rectifies the output from the switching transformer 13 into the amplitude required for charging. The output unit 15 then generates a charging voltage after carrying out smoothing of the power being output from the voltage doubler unit 14.
The comparer 12 receives feedback of the charging voltage being output, so that charging power can be output to within an acceptable error range with respect to a preset reference value.
Referring to FIG. 1B, a bias transfer power generating unit includes, in a similar manner as the charging power generating unit explained above, a controller 21, a comparer 22, a switching transformer 23, a voltage doubler unit 24, and a transfer power output unit 25. The difference is that the transfer bias voltage is less in magnitude than that used in the charger, and is modulated to be supplied to the transfer unit at regular time intervals.
Differences in output power and control signals used for charging and transfer have necessitated the use of multiple power supplies. That is, conventionally, each of the components requires its own power supply.
In order to solve the problems of the conventional art described above, conventional systems use a circuit to generate transfer power directly from an output from a high voltage charging power generator without regard to the effect of variations of the power demands of one the components has on the power demands of another of the components. Since, in these systems, charging power directly influences transfer power, a change in the charging power level results in a change in the transfer power, also. Furthermore, this type of power supply system is particularly inefficient in a color printing application, which requires an increased number of components.